The present invention relates to a method for enhancing growth in horticultural plants in sub-optimal light conditions by applying to the surface of the plant an effective amount of an ultrafine, dry ground, calcium carbonate derived from calcite. Ultrafine, dry ground, calcium carbonate derived from calcite has been found to exhibit high transmission and low reflectance of light in the photosynthetically active radiation (“PAR”) and ultraviolet (“UV”) wavelengths. It is generally accepted that PAR wavelengths are between 400 nm and 700 nm, and that UV wavelengths are between 10 nm and 400 nm. By “sub-optimal light conditions” is meant excess or insufficient sunlight for optimal photosynthesis.
At the higher end of sunlight exposure intensity excess sunlight can damage plant tissue through excess absorbence by the plant's photosynthetic pigments. When light intensity exceeds the light saturation point for photosynthesis, regardless of light type, photosynthetic pigments are damaged. Both the xanhophyll cycle and the antioxidant system of the plant provide some natural protective response to such photooxidative stress (“up-regulation”), but this natural up-regulation often does not provide enough protection against photooxidative damage. Damage to the oxygen evolving complex (“OEC”) by high temperatures makes the photosystem II protein complex (“PSII”) more sensitive to high light damage. Thus, the resulting damage caused by such excess sunlight causes a loss of chlorophyll production.
At the lower end of sunlight exposure intensity insufficient or low light intensity sunlight contributes to a loss of chlorophyll production.
U.S. Pat. No. 6,110,867 describes a method for providing enhanced photosynthesis of a horticultural crop “by increasing carbon dioxide assimilation.” See the Reexamination Certificate issued under 35 U.S.C. 307 for this patent. The method comprises applying to the surface of the crops an effective amount of one or more “highly reflective” finely divided particulate material having a particle size of below about 3 microns. The useful particulate materials specified in this patent include calcium carbonate, mica, kaolin, bentonite, clays, pyrophyllite, silica, feldspar, sand, quartz, chalk, limestone, diatomaceous earth, baryle, aluminum trihydrate, titanium dioxide and mixtures thereof. These particulate materials are stated to be hydrophilic, but can be coated with a hydrophobic wetting agent to cause the hydrophilic core material to have a hydrophobic outer surface. However, as this patent admits, increasing the reflectivity of a plant's surface causes a reflection of PAR light which reduces photosynthesis. See column 1, lines 60-67.